1. Field of the Invention
The present invention relates to plastic valve bags, which may or may not have outer paper surrounding bag structures, for the containment of particulate materials.
2. The Prior Art
A plastic valve sack/bag is produced by forming specially formulated plastic sheet (film) over a series of folding frames to create the desired bag configuration. Heat seals are made using hot metal sealing bars at both the end of the bag to create a bottom seal and in the face of the bag using a U sealer to create the valve opening. An anti-sift flap is provided in the valve opening area to discourage the sifting of product from the bag. Air is vented from the customer filled bag through both the valve opening and through a series of paths created by the unique U seal configuration. In addition, the bag, if of the multi-layer style, may be provided with pluralities of small holes that are misaligned, from layer to layer, to likewise permit air escape, but prevent sifting, in view of the tortuous path the particles would have to take from the interior, through the several layers, to the outside. During air evacuation and subsequent transportation/storage the filled product (typically solid particulate material) can sift out through the valve opening. This is an undesirable effect for several reasons including economic loss (loss of product), environmental (product spills into the environment), safety (potential slipping or contamination hazard), and aesthetics where many retailers do not want their store floors covered with leaking product.
Bags having internal anti-sift flaps are known. Examples of such bags, which are provided with paper outer structures, are shown in U.S. Pat. Nos. 5,516,210; 5,806,982; and 6,092,930. In these references, bags are shown having internal anti-sift flaps associated with valve tube structures not formed as part of the bags, per se. These valve tube structures are located in the top (or bottom) end regions of the bags, with portions of the valve tubes extending outwardly from a front (short) wall of the bag. The valve tubes have outer support portions fabricated from paper, with sealable plastic liner portions. Positive sealing of the outwardly extending portions of the valve tubes is accomplished by heat or ultrasonic sealing.
However, such sealing techniques are difficult or not possible, when no outwardly projecting valve tube is provided, or when the bag is fabricated in its entirety from plastic (which may not be of a kind that is amenable to heat or ultrasonic sealing), or when the valve is located in a position away from a peripheral “edge” region of a bag.
For example, valve bags, fabricated entirely from plastic are known, wherein the valves are located in a face (large area side) of a bag, at a location away from the top, end or side edges of the face, in a region where there is the edges of the tube forming the bag overlap, the valve being formed essentially as a gap in the seal that forms the bag.
It is desirable to provide a structure that provides for the positive sealing of such a valve bag, after filling, to substantially or entirely preclude sifting of product from the bag.
It is also desirable to provide a method for positive sealing of such valve bags, that does not require the external application of energy such as heat or ultrasonic vibrations.
These and other desirable characteristics of the present invention will become apparent in view of the present specification and drawings.